a -= n / 180 * Math.PI;

public void rotate(double x, double y, double cx, double cy, double n) {
      double dx = x - cx; // calculate current angle of drawn line (the bow?)
      double dy = y - cy;
      double r = Math.sqrt(dx*dx + dy*dy);
      double a = Math.atan2(dy, dx); // angle is known now in rad

      a -= n / 180 * Math.PI; // rotation in rad is converted to rad... uhm, yeah. And then subtracted from the computed angle of the line... am I getting this wrong?
      this.x = cx + r * Math.cos(a);
      this.y = cy + r * Math.sin(a);
   }
   
   public void render(Graphics g) {
      //image.draw((float)x, (float)y);
      g.setColor(Color.red);
      g.drawLine((float)x, (float)y, (float)x2, (float)y2);

   }
   
   public void update(GameContainer container) {
      Input input = container.getInput();
      rotation = Math.atan2( input.getMouseY() - 600/2, input.getMouseX() - 800/2 ); // mouse coordinates relative to center of the screen used for getting the angle between normal position without rotation and rotation to current mouse position
      
      rotate(x, y, x2, y2, rotation); // method for rotation. Uses line start and end point and rotation angle as inputs...
   }

private void renderBlock(Block.BlockType type) {
     
      GL11.glTexCoord2f(0.0f, 0.0f);
      off_glVertex3f(-0.5f, -0.5f, 0.5f);   // Bottom Left Of The Texture and Quad
      GL11.glTexCoord2f(1.0f, 0.0f);
      off_glVertex3f( 0.5f, -0.5f, 0.5f);   // Bottom Right Of The Texture and Quad
     [...]
      off_glVertex3f(-0.5f, 0.5f, -0.5f);   // Top Left Of The Texture and Quad      
        GL11.glEnd(); // this one here ########################
        glColor3f(1,1,1);
   }

uniRay.setPosition(-pos.getX(),-pos.getY(),-pos.getZ());
      uniRay.setDelta((float)Math.sin(Math.toRadians(-rotY))*(float)-Math.cos(Math.toRadians(-rotX)),
                           (float)Math.sin(Math.toRadians(-rotX)),
                           (float)-Math.cos(Math.toRadians(-rotY))*(float)Math.cos(Math.toRadians(-rotX)));
      uniRay.scalarProduct(RAY_LENGTH); // change length of the uniform vector

// texture stuff
      TextureManager tM = TextureManager.getTextureManager();
      if(tM.getTexture("tex") == null){
         tM.addTexture("tex", "img/testTextur.png");
         tM.addTexture("tex2", "img/testTextur2.png");
         tM.addTexture("controls", "img/controls_eng.png");
      }
      tex = tM.getImage("tex2"); // tex is an attribute of type Image
      tM.bind(tex);

import org.lwjgl.opengl.GL11;

public class Texture{
   
   private int texID;
   private int width;
   private int height;
   
   public Texture(int id, int w, int h){
      texID = id;
      width = w;
      height = h;
   }
   
   public int getImageWidth(){
      return width;
   }
   
   public int getImageHeight(){
      return height;
   }
   
   public int getTextureID(){
      return texID;
   }
   
   public void release(){
      GL11.glDeleteTextures(texID);
   }
}

public void addTexture(String name, String path){
      if(dataBase.containsKey(name))
         System.err.println("Image with key " + name + " already in database!");
      else{
         Texture tex = loadTexture(path);
         dataBase.put(name, new Image(tex)); // #### HERE ######## new Image(tex)
      }
   }